Faulty desktop PSU? Replace PSU or system?

Hello all.

My wife's desktop has started to behave (more) erratically as of a couple of days ago. I am looking for advice as if my diagnosis is correct and on what to do.

For several years the desktop would routinely do a double boot up, never understood why, but it was working anyway.

I think 1 or 2 years ago or maybe longer it would also start on its own. Oddly this would often happen as I was launching World of Warcraft on my laptop...

Then a few days ago it started getting more weird : the desktop was obviously on but all the peripherals were dark (RGB keyboard and mouse dark and unresponsive, dark screen). After that I checked the peripherals and the inside of the desktop as well as all the USB ports. All fine but after putting everything back together it will not boot up reliably. Some times the PSU is absolutely unresponsive and only after fiddling with its switch and the power cord's will it finally power up and boot. Sometimes it also takes a while for the monitor to light up.

I think the PSU is getting old, as the system is a 2011 vintage Sandy Bridge i5 computer shop prebuilt.

I have no reason to think the load on it is too heavy, as the only changes I made were last year when I added 4GB of RAM, a system SSD and replaced the original GTX 550 Ti with a GTX 1050 Ti.

I'm currently wondering wether to replace the PSU and maybe case (hers is a big ugly one), and/or upgrade from that and the HDD, SSD and GPU to a new Coffee Lake MOBO/CPU. Or simply going for some prebuilt in which I'd stick her GPU, pity I missed already a number of nice deals on some nice Coffee Lake prebuilt with GTX 1060 6GB...

 

Start by getting a new PSU, see what happens. If you have no luck with the new PSU, then get a new system (You'd already have the new PSU at that point anyways).